1. Field of the Invention
The present invention relates to a valve device which is operated by an electromagnetic actuator of an on-off functioning type.
2. Description of the Prior Art
As is well known in the art, in most internal combustion engines, opening and closing of intake and exhaust valves have been heretofore generally performed by cams. The profile of the cam is precisely made so that the valve is smoothly and gently opened and closed even when the engine operates at a high speed. Specifically, the profile of the cam for closing the valve has a damping curve so that the valve is made to smoothly and gently take the valve seat but is prevented from abruptly seating thereon.
However, as electronics is applied to automobiles in recent years, a technique is being developed which uses an electromagnetic actuator so as to effectively operate intake and exhaust valves and control the timing of opening and closing of the valves in accordance with the operating condition of the engine. In this instance, the valve is operated by on and off operation of the electromagnetic actuator so that when the actuator is fed with electric current, the valve is opened by the actuator and when the feed of electric current to the actuator is cut off, the valve is closed by a return spring. However, the valve has not been provided with an expedient which has the valve smoothly and gently take the valve seat.
For this reason, it has been unavoidable that the valve is closed by colliding against the valve seat. Specifically, an exhaust valve exposed to combustion gas having a high temperature has suffered severe wear and tear so that the life of the valve has been sharply shortened. Also, great vibration and noise have been produced because of collision of the valve with the valve seat.